On February 6, Queen Elizabeth will be the first British monarch to mark her Sapphire Anniversary, marking 65 years on the throne.

But in a reign of record-breaking jubilees and milestone birthdays (she turned 90 last year), this will be one anniversary that won’t be marked publicly.

February 6 is also the anniversary of the death of her father George VI, an event that made her monarch at age 25.

The Queen will do some work behind the scenes as she reads documents sent to her by government departments in her historic red boxes. There will also be a gun salute by the military in London’s royal parks and the Royal Mint has produced a commemorative set of coins. But there are no official outings or engagements planned, and she will spend the day “quietly,” a palace source tells PEOPLE, in part contemplating the anniversary of her father’s passing.

Being a Monday, she will have likely gone to church the previous day – possibly to St. Mary Magdalene – where her father’s body lay for two days before his casket was taken south to London for his funeral.

The Queen, knowing the importance of symbols and color hints (she wore the same shade of purple as the new Elizabeth Line brand when she opened the railway), did give a little nod to the momentous year ahead, when she appeared in public for the first time after her recent heavy cold in a sapphire outfit while on her way to church.

But royal insiders aren’t surprised she will play down the anniversary on Monday. “She’s naturally shy and is the opposite of showy,” says royal historian Robert Lacey. “And, of course, the anniversaries of the accession remind her of her father’s premature death.

“There is only so many of these landmark dates that people will want to mark. I”m sure she would rather people were asking why isn’t it being celebrated rather than, ‘Oh no, not another royal anniversary.’ She always plays safe — and that is a good instinct.”

Lacey adds that anniversaries began being celebrated by Queen Victoria and were encouraged by jewelry merchants and anniversary card publishers.

“The Queen is always wary of the commercial aspects, and doesn’t want to appear ‘on the make’ — though she doesn’t mind if charities use anniversaries to raise money,” he says. “She’s got a well-developed sense of not wanting to exploit these royal anniversaries.”